Hottest Planet Ever Discovered

An artist's impression of the extrasolar planet HD 189733b, seen here with its parent star looming behind--astronomers said its sunset looks similar to a hazy red sunset on Earth. The planet is slightly larger than our own solar System's Jupiter, and its atmosphere is a scorching eight hundred degrees Celsius.

Credit: ESA/NASA/Frederic Pont, Geneva University Observatory

In the hunt for extrasolar planets, a new find is shattering
records left and right.

A planet called WASP-12b is the hottest planet ever
discovered (about 4,000 degrees Fahrenheit, or 2,200 degrees Celsius), and
orbits its star faster and closer in than any other
known world.

This sizzling monster whips its way around its parent star
about once a day (for comparison, the fastest-circling
planet in the solar system, Mercury, orbits the sun once every 88 days).

To make such swift progress, the planet circles extremely
close-in to its star ? about 2 percent of the distance from the Earth to the
sun, in fact, or 2 million miles (3.4 million kilometers).

"WASP-12b is incredibly interesting, because we're at a
stage in the study of exoplanets where we're finding
new examples all the time," said Don Pollacco of Queen's University in
Northern Ireland, who is a project scientist for the SuperWASP (Super Wide
Angle Search for Planets) project that discovered WASp-12b. "It was
exciting because it was the shortest period and the hottest planet, but I
suspect there are even shorter period planets, and hotter planets to
come."

WASP-12b is a gaseous planet, about 1.5 times the mass of
Jupiter, and almost twice the size.

The planet, which orbits a star 870 light years from Earth,
is especially notable because it pushes the bounds of how close planets can
ever come to their stars without being destroyed.

"There is a limit because as a planet gets closer to
its star, the radiation field gets more and more intense, and at some point that
whole planet will be evaporated by its star," Pollacco told SPACE.com.
"Before, some people thought it was impossible to find planets that had 1-day
periods. I think it's so early in the whole subject, and it takes a number of
objects before you can start setting limits."

The planet is also so hot that its temperature matches that
of some stars. This planet, however, is definitely not a star because its
mass isn't nearly large enough for the internal thermonuclear reactions that
define stars.

WASP-12b is one of only about 50 extrasolar planets that
have been detected through the transit method, meaning they were found by
measuring the dip in brightness of their parent star as they pass in front of
it and block part of its light.

"It's an incredibly hard way to detect planets, because
the size of this dip when it moves across the star is very small,"
Pollacco said. "These objects are difficulty to find, but they're incredibly
valuable when you do find them because they tell you so much."

The transit method allows astronomers to not only note the
presence of a planet, but estimate its size, mass and density. And by
estimating its distance from its star, researchers can deduce its rough
temperature, because the closer in an object is, the hotter it gets.

All the information scientists have so far about WASP-12b
indicates that this fiery ball cozily circling its star is an odd case. Yet
discoveries like this raise the question, are planets like this in fact more
common in the universe than planets
like Earth?

"Is our solar system the freak, or are these other
solar systems the freaks?" Pollacco said. "Who knows? I suspect that
for life to evolve as we know it, you have to have a special set of
circumstances come together to produce very specific conditions."

The SuperWASP project, based in the UK, uses telescopes in
Spain's Canary Islands and in South Africa to scan the sky searching for
distant planets that cross in front of their stars.

The discovery of WASP-12b was first announced in April 2008,
though its distinction as the hottest and fastest-orbiting exoplanet was
confirmed Oct. 11 at the annual meeting of the American Astronomical Society?s
Division for Planetary Sciences by co-discoverer Leslie Hebb of the University
of St. Andrews in Scotland.

Clara has been SPACE.com's Assistant Managing Editor since 2011, and has been writing for SPACE.com and LiveScience since 2008. Clara has a bachelor's degree in astronomy and physics from Wesleyan University, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what her latest project is, you can follow Clara on Google+.